1. Field of the Invention
This invention relates generally to telephone answering devices, and more particularly to a system for screening incoming calls to discriminate between desired and undesired calls.
2. Description of the Prior Art
Telephone users today have a variety of systems for answering incoming calls. For example, telephone answering devices are commonly used to automatically answer the telephone with announced instructions and then record a message from the caller. These answering devices can be expensive, and are used principally for answering the telephone when the party being called is absent.
There are many situations at home and in an office where the party being called is present but would like to have the incoming telephone calls screened, to avoid answering wrong numbers and to answer only those calls that might be important while avoiding other calls. Answering services are expensive and more appropriate for business use. They are not practical for use with a home phone to screen incoming calls. Telephone answering devices also are not practical in many cases for screening incoming calls.
Some telephone screening devices have been proposed for discriminating between desired and undesired incoming calls. Some of these devices are activated by an encoded signal from the caller to indicate to the party being called the presence of a desired call. One of these screening devices, disclosed in U.S. Pat. No. 4,074,078 to Jansen, requires use of a hand-held key device such as a beeper issued by the user to each person from whom it may be desirable to receive telephone calls. The caller carries the beeper and uses it to emit an audible tone of a particular frequency detected by the phone call screener to indicate the presence of a desired call. Such an arrangement can be impractical because it can be expensive to issue separate beepers to various persons who may call. There can also be instances in which the person desiring to call may not have the beeper at hand.
Other telephone screening devices are not totally desirable because callers are aware that a screening device is attached to the receiving telephone. For example, the screening device disclosed in U.S. Pat. No. 3,514,548 to De Meo mechanically lifts the receiver and if the proper code is not transmitted, the receiver hangs up, thus terminating the call. This is not only discourteous but also informs callers that the incoming calls are being screened. There are many instances where a person wants callers (other than those from whom calls are considered important) to be totally unaware that incoming calls are being screened.